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How to Interconnect to Transmission

Once you have decided that you are ready to interconnect to the transmission system, you can begin the process.

After the submittal of an interconnection request, most projects take upwards of four years to interconnect. However, complexities related to the proposed point of interconnection, network and distribution upgrade construction, permitting, siting and numerous other factors can cause projects to become unforeseeably delayed.

We welcome the opportunity to perform detailed analysis related to your project interconnection via a design and engineering agreement once a system impact study is completed.

Project Phase

The interconnection project phase starts when you submit an interconnection request to ISO New England via the Interconnection Request Tracking Tool (IRTT).

Videos on how to complete the submission can be found in the ISO New England Interconnection Process Guide under submit your interconnection request.

More information is also available on the Undergo the Interconnection Study Process page of the ISO New England Interconnection Process Guide.

As study agreements are signed, we will provide cost estimate details to perform the study. By request, we can break out the cost estimates into the following categories:

  • Labor
  • Materials
  • Contractor Services
  • Engineering Services
  • Other Outside Services
  • Contractor Labor
  • Environmental Outside Services
  • Licensing and Permitting 

Required ISO New England deposits

Project TypeInitialFeasibility StudySystem Impact Study Facilities Study
Large Generators (> 20 MW) $50,000 (becomes
nonrefundable 10 business days after scoping meeting)
100% of the estimated study costs Greater of 100% of the estimated study costs or $250,000 Greater of 25% of the estimated cost of the study or $250,000
Small Generators (≤ 20 MW) $2,500 (nonrefundable) Lesser of 50% of the good faith estimated study costs or earnest money of $1,000 50% of the estimated cost for the transmission portion of the study and 100% of the estimated cost for the distribution portion 100% of the estimated study 
Elective Transmission Upgrades $50,000 (becomes
nonrefundable 10 business days after scoping meeting)
100% of the estimated study costs Greater of 100% of the estimated study costs or $250,000 Greater of 25% of the estimated cost of the study or $250,000

As of April 1, 2023 pursuant to Schedule 22, 23 & 25 of the OATT

Early assessment

Pursuant to Schedule 23 of the Open Access Transmission Tariff (OATT), prospective interconnection customers (for small generating facilities <=20MW ) have the option to submit a formal pre-application request to ISO-NE to obtain a pre-application report on a proposed project in question at a specific site.

We will generate a report using existing system data that reflects the best available information at the time of reporting. The items to be included in this report include but are not limited to:

  • Total capacity of the substation or transmission line based on normal operating ratings, pursuant to operating and planning manuals and procedures likely to serve the proposed point of interconnection (POI)
  • Existing aggregate generation capacity (in MW) interconnected to a substation or transmission line likely to serve the proposed POI
  • Approximate transmission line distance between the proposed POI and the substation in question

This report is non-binding and does not confer any rights to any of the parties involved, as the interconnection customer must still successfully apply to interconnect with the New England transmission system.

The deposit for the pre-application is $500.

A full comprehensive list of all items pursuant to Schedule 23 pre-application can be found in the pertinent schedule of the tariff.

Infrastructure Coordination

Once an interconnection agreement has been signed, the infrastructure coordination phase will begin.

During this time, we will conduct periodic coordination meetings between Eversource and the interconnection customer.

The first meeting will be a kick-off to discuss the project construction timeline as identified in the interconnection agreement.

In addition to project construction, the following occurs at this time:

  • Financial assurance, as identified in Schedule 11, 22 ,23, or 25 of the OATT, will be assessed (see Supplemental Manual for Credit and Security Requirements for Generator Interconnections for details) .
  • Discussions regarding siting expectations. We will coordinate with the customer early in the process to develop an overall project siting plan that encompasses both interconnecting customer interconnection facilities as well as interconnecting transmission owner transmission facilities. Please contact us for additional questions or details.
  • Operation and Maintenance (O&M) assigned to the project will be calculated based on FERC Form 1 Data and the estimated investment cost of facilities.